Police campaign means proper documents must be carried at all times, Cui Jia, He Na and Peng Yining report in Beijing.The 26-year-old US citizen, who has been in China since 2008, had not felt the need to register with the police before a 100-day crackdown was launched on May 15 to combat what's become known as the "three illegals". This refers to foreigners who have entered illegally, overstayed their visa or been employed without obtaining a work permit."I heard about the crackdown when I was in the US and then remembered that I hadn't registered with the local police, as required after moving to my new apartment. I really don't want to get into trouble," he said. "I know when the Chinese authorities use the term 'crackdown', they mean business."